As a result of peace talks with the Colombian government, Marín Arango became part of the leftist Patriotic Union (UP) party, coordinating the UP's activities in Department of Caqueta . Marín Arango first served as councilman and then as congressman in the Colombian Congress representing Caquetá.[1][2]

The UP party was subjected to persecution by different paramilitary groups, drug lords and death squads that saw the party as a threat as the political branch of the FARC.[2]

By 1988, Iván Márquez had left the UP and returned to FARC as block commander, overseeing activities in the departments of Huila, Caquetá and Putumayo.[1]

After the 1990 death of Jacobo Arenas, Márquez joined the Secretariat, the highest command of the organization. During the mid-1990s, he was transferred to Colombia's northwest in order to reorganize FARC forces after paramilitary attacks.[1]

Recent documents obtained from the computer of slain FARC chieftain Ivan Rios revealed that he also led FARC's efforts to infiltrate universities and high schools. "Through the creation of two student federations, some academics and other secondary officials, and by the infiltration of already existing university movements" the FARC sought to penetrate centers of learning, [Colombian DAS intelligence director María del Pilar] Hurtado told Spanish news agency EFE. Colombian armed conflict.[3]

In November 2007 Márquez was sent to Venezuela to meet with Venezuelan President Hugo Chavez. At the time, Chavez was mediating between the government of Colombia and the FARC to agree on a deal to liberate the hostages held by the FARC and the liberation of some 500 guerrillas imprisoned by the government of Colombia, after years of combats in the Colombian armed conflict.[4]

According to the US Department of State, he oversaw loading of planes carrying 600-1200 kilograms of cocaine and the receipt of money and automatic weapons as payment. The state department also alleges him of setting the FARC's cocaine policies for directing and controlling the production, manufacture, and distribution of hundreds of tons of cocaine to the United States and the world; the "taxation" of the drug trade in Colombia to raise funds for the FARC; and the murder of hundreds of people who violated or interfered with the FARC's cocaine policies and/or political agenda. They are offering a reward of up to $5 million for information leading to his arrest and/or conviction[5]